Search

We have shown that elevated HDL cholesterol (HDL-C) levels (≥80 mg/dL) associate with increased CAD risk in women with T1D. Furthermore, HDL-C levels are not necessarily cardioprotective in nondiabetic individuals, suggesting that the cholesterol content of HDL does not accurately assess CAD risk. We thus determined whether two other HDL metrics, HDL particle concentration (HDL-P) and cholesterol efflux capacity (CEC), predicted incident CAD in a large cohort of childhood onset T1D (n=550). At baseline, mean age was 27.8 yrs, T1D duration was 19.6 yrs and 49% were women. HDL-P was assessed by calibrated ion mobility analysis and CEC was quantified with validated assays in cAMP stimulated J774 cells and in ABCA1-expressing BHK cells. CAD was defined as CAD death, myocardial infarction and/or revascularization. During a median follow-up of 26 yrs, we observed 203 incident CAD cases (36.9%). At baseline, incident cases were older, more likely to have smoked, have hypertension, longer duration of T1D, higher non-HDL-C and markers of kidney disease and inflammation. Cases were also more likely to have lower HDL-P concentrations but similar CEC to non-cases. Cox models with backward elimination were constructed for each HDL metric, allowing for potential confounding variables, including HDL-C. In separate multivariable models, higher concentrations of total HDL-P (T-HDL-P, HR=0.88, 95% CI: 0.83-0.92) and 3 major HDL subpopulations - small (S-HDL-P, HR=0.78, 0.67-0.92), medium (M-HDL-P, HR=0.79, 0.71-0.88) and large-sized (L-HDL-P, HR=0.74, 0.61-0.89) particles - associated with a lower CAD incidence whereas HDL-C did not. Higher total CEC in J774 cells also predicted lower CAD risk (HR=0.74, 0.55-0.996) after similar adjustments, but became non-significant after further adjusting for HDL-P. ABCA1-specific CEC did not predict CAD. Our results suggest that increased HDL-P levels are cardioprotective in T1D, in contrast to HDL-C and CEC which did not independently predict CAD. Disclosure T. Costacou: None. T. Vaisar: Consultant; Self; AstraZeneca. K. Bornfeldt: None. T. J. Orchard: None. J. Heinecke: None. Funding National Institutes of Health (HL130153, DK34818)

The increased cardiovascular disease (CVD) risk associated with type 2 diabetes (T2D) is likely due in part to diabetic dyslipidemia—a condition characterized by elevated plasma levels of triglyceride‐rich lipoproteins (TRLs), smaller denser LDL particles, and decreased HDL cholesterol (1,2). Lifestyle modifications and statins are first-line interventions for CVD risk reduction in individuals with T2D, but such individuals remain at considerable risk for cardiovascular events (3). This residual CVD risk appears to be linked to abnormal metabolism of TRLs (3)—chylomicrons, VLDL, and their respective remnant lipoprotein particles (RLPs), many of which are present as intermediate-density lipoproteins (4). Thus, there is a need for developing effective and safe alternative approaches/medications to prevent and reduce diabetic dyslipidemia. In this issue of Diabetes , Roger et al. (5) report a potential new therapeutic strategy to simultaneously reduce LDL and VLDL levels by using a hybrid compound that demonstrates dual inhibition of cannabinoid-1 receptor (CB1R) and inducible nitric oxide synthase (iNOS) in a mouse model. The elevated TRLs in T2D are generally attributed to hepatic overproduction of apolipoprotein B (APOB)-containing VLDL, increased intestinal secretion of APOB48 (a truncated form of APOB100 in chylomicrons and their remnants), and dysregulated clearance of TRLs (1,2,6,7), as shown by Fig. 1. Insulin resistance and the resulting elevated fatty acids are believed to be responsible for the abnormal TRL metabolism in T2D (1,2,7). For example, inhibition of the transcription factor FoxO1 by insulin-induced Akt activation represses expression of microsomal triglyceride transfer …

Obesity is associated with metabolic syndrome and gliosis, the activation of microglia (brain macrophages) and astrocytes, in the mediobasal hypothalamus (MBH) of humans and rodents. Similarly, hypogonadism in males is associated with increased susceptibility to weight gain, metabolic syndrome and MBH gliosis. Interventions that reduce glial activation in rodents result in protection from diet-induced obesity. Thus, we hypothesize that the combination of low testosterone and western diet causes gliosis, which in turn increases obesity susceptibility. To test this hypothesis in a rodent model, we combined gonadectomy (GDX) or sham surgery with high-fat diet (HFD) feeding in adult male mice. GDX and HFD feeding synergistically induced a striking activation of MBH astrocytes along with increased numbers of MBH microglia. This gliosis response was reversed to sham levels by testosterone replacement. After only 4 weeks of HFD feeding, differences in adiposity between GDX and sham groups were minimal with only a mild worsening of glucose tolerance. Thus, testosterone deficiency combined with HFD exposure elicits gliosis prior to substantial weight gain, suggesting a direct impact on glial cell function. To characterize the transcriptional response to testosterone deprivation and HFD exposure, we have developed mouse strains with GFP-tagged ribosomes (L10A) in astrocytes and microglia to allow purification of glial cell-specific mRNA from whole hypothalamic tissue samples (tagged ribosome affinity purification (TRAP)). In preliminary analyses, we have confirmed >10-fold enrichment of cell-specific mRNAs with de-enrichment of neuronal transcripts. These studies help reveal novel mechanisms by which hypogonadism increases the predisposition to metabolic disease. Disclosure M.D. Dorfman: None. J. Frey: None. K.M. Ness: None. A. Niraula: None. J.E. Kanter: None. K. Bornfeldt: None. K. Rubinow: None. E. Schur: None. J. Thaler: None. Funding American Heart Association (16SDG27010018); Diabetes Research Center (P30DK017047); Novo Nordisk (A116079); National Institutes of Health (R01DK119754)

Although it has long been proposed that HDL is dysfunctional in type 1 diabetes (T1D), this hypothesis has not been formally tested in large cohorts using validated functional and biochemical HDL metrics. We therefore determined whether HDL particle concentration (HDL-P) and function differed between 187 middle-aged adults with childhood-onset T1D (mean age 51 years, T1D duration 43 years, 53% women) and 200 individuals with normal glucose tolerance (NGT) of similar age and sex distribution. HDL-P was assessed by calibrated ion mobility analysis. HDL function, i.e., serum HDL cholesterol efflux capacity, was quantified in J774 cells using a validated assay. Separate stepwise linear regression models were constructed for each HDL metric, allowing for T1D status and potential confounding factors, including HDL cholesterol (HDL-C). The presence of significant effect modification by sex was evaluated. After adjustment, the concentrations of total (T-HDL-P; β=-0.44, p=0.09) and medium-sized (M-HDL-P; β=-0.84, p In conclusion, lower levels of T-HDL-P and M-HDL-P in T1D may explain in part the higher cardiovascular risk in T1D, as these metrics were recently shown to be associated with protection from vascular complications. The lack of a difference in M-HDL-P by sex in T1D may contribute to the loss of cardioprotection associated with female sex. Disclosure T. Costacou: None. T. Vaisar: Consultant; Self; AstraZeneca. J. Ju: None. K. Bornfeldt: None. T.J. Orchard: None. J. Heinecke: None. Funding National Institutes of Health (HL130153, DK34818)

Cardiovascular disease caused by atherosclerosis is the leading cause of mortality associated with type 2 diabetes and metabolic syndrome. Insulin therapy is often needed to improve glycemic control, but it does not clearly prevent atherosclerosis. Upon binding to the insulin receptor (IR), insulin activates distinct arms of downstream signaling. The IR-Akt arm is associated with blood glucose lowering and beneficial effects, whereas the IR-Erk arm might exert less desirable effects. We investigated whether selective activation of the IR-Akt arm, leaving the IR-Erk arm largely inactive, would result in protection from atherosclerosis in a mouse model of metabolic syndrome. The insulin mimetic peptide S597 lowered blood glucose and activated Akt in insulin target tissues, mimicking insulin’s effects, but only weakly activated Erk and even prevented insulin-induced Erk activation. Strikingly, S597 retarded atherosclerotic lesion progression through a process associated with protection from leukocytosis, thereby reducing lesional accumulation of inflammatory Ly6Chi monocytes. S597-mediated protection from leukocytosis was accompanied by reduced numbers of the earliest bone marrow hematopoietic stem cells and reduced IR-Erk activity in hematopoietic stem cells. This study provides a conceptually novel treatment strategy for advanced atherosclerosis associated with metabolic syndrome and type 2 diabetes.

Diabetes is now a pandemic disease. Moreover, a large number of people with prediabetes are at risk for developing frank diabetes worldwide. Both type 1 and type 2 diabetes increase the risk of atherosclerotic cardiovascular disease (CVD). Even with statin treatment to lower LDL cholesterol, patients with diabetes have a high residual CVD risk. Factors mediating the residual risk are incompletely characterized. An attractive hypothesis is that remnant lipoprotein particles (RLPs), derived by lipolysis from VLDL and chylomicrons, contribute to this residual risk. RLPs constitute a heterogeneous population of lipoprotein particles, varying markedly in size and composition. Although a universally accepted definition is lacking, for the purpose of this review we define RLPs as postlipolytic partially triglyceride-depleted particles derived from chylomicrons and VLDL that are relatively enriched in cholesteryl esters and apolipoprotein (apo)E. RLPs derived from chylomicrons contain apoB48, while those derived from VLDL contain apoB100. Clarity as to the role of RLPs in CVD risk is hampered by lack of a widely accepted definition and a paucity of adequate methods for their accurate and precise quantification. New specific methods for RLP quantification would greatly improve our understanding of their biology and role in promoting atherosclerosis in diabetes and other disorders.

People with T1D have higher HDL cholesterol (HDLc) yet are more insulin resistant and have increased cardiovascular disease (CVD) risk than people without diabetes. We hypothesized that HDL is dysfunctional in people with T1D, explaining this paradox. We examined the association between eIS, serum HDL CEC, and HDL subspecies in adults with T1D. This study was conducted in a sub-cohort (N=134) randomly selected from the Coronary Artery Calcification in type 1 diabetes study (N=652). eIS was calculated using a validated equation that includes waist circumference, triglycerides, adiponectin, diastolic blood pressure and insulin dose. We quantified CEC from a macrophage cell line (J774) and through the cholesterol transport proteins ABCA1 and ABCG1 and HDL particle concentration and size using calibrated ion mobility analysis. The analyzed HDLs were extra small (XS-HDL), small (S-HDL), medium (M-HDL) and large (L-HDL) populations. Associations were assessed by multivariable linear regression. J774 and ABCA1 CEC were negatively associated with eIS, as was S-HDL (Table). eIS positively associated with L-HDL, whereas other HDL metrics were not associated with eIS. Higher eIS associated with fewer S-HDL particles and reduced macrophage- and ABCA1-mediated CEC, suggesting novel interactions among insulin sensitivity and HDL metrics, which may contribute to CVD risk in T1D. Disclosure T. Buckner: None. K. Bornfeldt: None. J. Heinecke: None. T. Vaisar: Consultant; Self; MedImmune. Research Support; Self; MedImmune. J.K. Snell-Bergeon: None. Funding American Diabetes Association (7-13-CD-10 to J.K.S-B.)

The risk of cardiovascular events in humans increases in the presence of type 1 or type 2 diabetes mellitus, in large part due to exacerbated atherosclerosis. Genetically engineered mouse models have begun to elucidate cellular and molecular mechanisms responsible for diabetes-exacerbated atherosclerosis. Research on these mouse models has revealed that diabetes independently accelerates initiation and progression of lesions of atherosclerosis and also impairs the regression of lesions following aggressive lipid lowering. Myeloid cell activation in combination with proatherogenic changes allowing for increased monocyte recruitment into arteries of diabetic mice has emerged as an important mediator of the effects of diabetes on the three stages of atherosclerosis. The effects of diabetes on atherosclerosis appear to be dependent on an interplay between glucose and lipids, as well as other factors, and result in increased recruitment of monocytes into both progressing and regressing lesions of atherosclerosis. Importantly, some of the mechanisms revealed by mouse models are now being studied in human subjects. This Perspective highlights new mechanistic findings based on mouse models of diabetes-exacerbated atherosclerosis and discusses the relevance to humans and areas in which more research is urgently needed in order to lessen the burden of macrovascular complications of type 1 and type 2 diabetes mellitus.

Rosiglitazone is an insulin-sensitizing agent that has recently been shown to exert beneficial effects on atherosclerosis. In addition to peroxisome proliferator–activated receptor (PPAR)-γ, rosiglitazone can affect other targets, such as directly inhibiting recombinant long-chain acyl-CoA synthetase (ACSL)-4 activity. Because it is unknown if ACSL4 is expressed in vascular cells involved in atherosclerosis, we investigated the ability of rosiglitazone to inhibit ACSL activity and fatty acid partitioning in human and murine arterial smooth muscle cells (SMCs) and macrophages. Human and murine SMCs and human macrophages expressed Acsl4, and rosiglitazone inhibited Acsl activity in these cells. Furthermore, rosiglitazone acutely inhibited partitioning of fatty acids into phospholipids in human SMCs and inhibited fatty acid partitioning into diacylglycerol and triacylglycerol in human SMCs and macrophages through a PPAR-γ–independent mechanism. Conversely, murine macrophages did not express ACSL4, and rosiglitazone did not inhibit ACSL activity in these cells, nor did it affect acute fatty acid partitioning into cellular lipids. Thus, rosiglitazone inhibits ACSL activity and fatty acid partitioning in human and murine SMCs and in human macrophages through a PPAR-γ–independent mechanism likely to be mediated by ACSL4 inhibition. Therefore, rosiglitazone might alter the biological effects of fatty acids in these cells and in atherosclerosis.

Hyperglycemia and hyperlipidemia are important risk factors for diabetes-accelerated atherosclerosis. Macrophage proliferation has been implicated in the progression of atherosclerosis. We therefore investigated the effects of hyperglycemia and hyperlipidemia on macrophage proliferation in murine atherosclerotic lesions and isolated primary macrophages. Hyperglycemic LDL receptor-deficient mice that were fed a cholesterol-free diet for 12 weeks did not have elevated cholesterol levels compared with nondiabetic mice, and there was no evidence of increased macrophage proliferation in atherosclerotic lesions. Moreover, elevated glucose levels did not increase proliferation of isolated mouse peritoneal macrophages. In contrast, hyperglycemic LDL receptor-deficient mice that were fed a cholesterol-rich diet showed increased cholesterol levels concomitant with macrophage proliferation in atherosclerotic lesions. Glucose promoted lipid and protein oxidation of LDL in vitro. Glucose-oxidized LDL resulted in phosphorylation of extracellular signal-regulated kinase and protein kinase B/Akt and stimulated proliferation of isolated macrophages. The mitogenic effect of glucose-oxidized LDL was mediated by CD36 and by extracellular signal-regulated kinase activation induced by protein kinase C-dependent and phosphatidylinositol 3-kinase-dependent pathways. Thus, hyperglycemia is not sufficient to stimulate macrophage proliferation in lesions of atherosclerosis or in isolated macrophages. A combination of hyperglycemia and hyperlipidemia, however, stimulates macrophage proliferation by a pathway that may involve the glucose-dependent oxidation of LDL.

Our goal was to determine the role of the p75 neurotrophin receptor (p75NTR) in the loss of islet sympathetic nerves that occurs during the autoimmune attack of the islet. The islets of transgenic (Tg) mice in which β-cells express a viral glycoprotein (GP) under the control of the insulin promotor (Ins2) were stained for neuropeptide Y before, during, and after virally induced autoimmune attack of the islet. Ins2-GPTg mice injected with lymphocytic choriomeningitis virus (LCMV) lost islet sympathetic nerves before diabetes development but coincident with the lymphocytic infiltration of the islet. The nerve loss wasmarked and islet-selective. Similar nerve loss, chemically induced, was sufficient to impair sympathetically mediated glucagon secretion. In contrast, LCMV-injected Ins2-GPTg mice lacking the p75NTR retained most of their islet sympathetic nerves, despite both lymphocytic infiltration and development of diabetes indistinguishable from that of p75NTR wild-type mice. We conclude that an nducible autoimmune attack of the islet causes a marked and islet-selective loss of sympathetic nerves that precedes islet collapse and hyperglycemia. The p75NTR mediates this nerve loss but plays no role in mediating the loss of islet β-cells or the subsequent diabetes. p75NTR-mediated nerve loss may contribute to the impaired glucose counterregulation seen in type 1 diabetes.

In combination with other factors, hyperglycemia may cause the accelerated progression of atherosclerosis in people with diabetes. Arterial smooth muscle cell (SMC) proliferation and accumulation contribute to formation of advanced atherosclerotic lesions. Therefore, we investigated the effects of hyperglycemia on SMC proliferation and accumulation in vivo and in isolated arteries and SMCs by taking advantage of a new porcine model of diabetes-accelerated atherosclerosis, in which diabetic animals are hyperglycemic without receiving exogenous insulin. We show that diabetic animals fed a cholesterol-rich diet, like humans, develop severe lesions of atherosclerosis characterized by SMC accumulation and proliferation, whereas lesions in nondiabetic animals contain fewer SMCs after 20 weeks. However, high glucose (25 mmol/l) does not directly stimulate the proliferation of SMCs in isolated arterial tissue from diabetic or nondiabetic animals, or of cultured SMCs from these animals or from humans. Furthermore, the mitogenic actions of platelet-derived growth factor, IGF-I, or serum are not enhanced by high glucose. High glucose increases SMC glucose metabolism through the citric acid cycle and the pentose phosphate pathway by 240 and 90%, respectively, but

Activation of AMP-activated protein kinase (AMPK) signaling reduces hepatic steatosis and hepatic insulin resistance; however, its regulatory mechanisms are not fully understood. In this study, we sought to determine whether vasodilator-stimulated phosphoprotein (VASP) signaling improves lipid metabolism in the liver and, if so, whether VASP’s effects are mediated by AMPK. We show that disruption of VASP results in significant hepatic steatosis as a result of significant impairment of fatty acid oxidation, VLDL-triglyceride (TG) secretion, and AMPK signaling. Overexpression of VASP in hepatocytes increased AMPK phosphorylation and fatty acid oxidation and reduced hepatocyte TG accumulation; however, these responses were suppressed in the presence of an AMPK inhibitor. Restoration of AMPK phosphorylation by administration of 5-aminoimidazole-4-carboxamide riboside in Vasp−/− mice reduced hepatic steatosis and normalized fatty acid oxidation and VLDL-TG secretion. Activation of VASP by the phosphodiesterase-5 inhibitor, sildenafil, in db/db mice reduced hepatic steatosis and increased phosphorylated (p-)AMPK and p-acetyl CoA carboxylase. In Vasp−/− mice, however, sildendafil treatment did not increase p-AMPK or reduce hepatic TG content. These studies identify a role of VASP to enhance hepatic fatty acid oxidation by activating AMPK and to promote VLDL-TG secretion from the liver.

Hyperglycemia and hyperlipidemia are important risk factors for diabetes-accelerated atherosclerosis. Macrophage proliferation has been implicated in the progression of atherosclerosis. We therefore investigated the effects of hyperglycemia and hyperlipidemia on macrophage proliferation in murine atherosclerotic lesions and isolated primary macrophages. Hyperglycemic LDL receptor-deficient mice that were fed a cholesterol-free diet for 12 weeks did not have elevated cholesterol levels compared with nondiabetic mice, and there was no evidence of increased macrophage proliferation in atherosclerotic lesions. Moreover, elevated glucose levels did not increase proliferation of isolated mouse peritoneal macrophages. In contrast, hyperglycemic LDL receptor-deficient mice that were fed a cholesterol-rich diet showed increased cholesterol levels concomitant with macrophage proliferation in atherosclerotic lesions. Glucose promoted lipid and protein oxidation of LDL in vitro. Glucose-oxidized LDL resulted in phosphorylation of extracellular signal-regulated kinase and protein kinase B/Akt and stimulated proliferation of isolated macrophages. The mitogenic effect of glucose-oxidized LDL was mediated by CD36 and by extracellular signal-regulated kinase activation induced by protein kinase C-dependent and phosphatidylinositol 3-kinase-dependent pathways. Thus, hyperglycemia is not sufficient to stimulate macrophage proliferation in lesions of atherosclerosis or in isolated macrophages. A combination of hyperglycemia and hyperlipidemia, however, stimulates macrophage proliferation by a pathway that may involve the glucose-dependent oxidation of LDL.